Growth of proteinase-positive and proteinase-negative lactococci strains in reconstituted goat and cow milks

Abstract

The growth of proteinase-positive Lactococcus lactis strains and the proteinase-negative variants was studied in reconstituted goat and cow milks at 90, 120 and 150 g·kg-1 total solids. pH change and lactic acid production were also compared in the two milks. Goat milk showed a higher buffering capacity than cow milk. The buffering capacity increased with the total solid contents in reconstituted milk. The proteinase-positive strains exhibited a higher maximum specific growth rate (µmax) and a higher acidification rate than the proteinase-negative variants. The bacterial count and the lactic acid concentration after 15 h of incubation were also higher with the proteinase-positive strains. The acidification rate and the lactic acid concentration after 15 h of incubation for all lac- tococci were significantly higher in reconstituted goat milk than in cow milk and increased with the total solid contents in reconstituted milk. The µ max and the viable counts obtained after 15 h of incu- bation for lactococci were relatively close in reconstituted goat and cow milks, with the exception of the Wg2S and Wg2L strains. For these strains, the µmax values were significantly higher in goat milk, but their bacterial counts after 15 h of incubation were lower in goat milk. An uncoupling was observed for these strains in goat milk. In general, reconstituted goat milk was an appropriate medium for the production of mesophilic lactic starters. However, to prevent an uncoupling with some strains such as the Wg2S and Wg2L strains, incubation in reconstituted goat milk at 21 °C should be shorter than incubation in reconstituted cow milk. goat milk powder / cow milk powder / growth of lactococci / reconstituted milk / proteinase- negative variants